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On the Impact of Ambient Stratification on Bottom Gravity Currents

On the Impact of Ambient Stratification on Bottom Gravity Currents. Tamay M. Ö zg ö kmen CPT Workshop II November 2004, RI. Progress Report:.

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On the Impact of Ambient Stratification on Bottom Gravity Currents

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  1. On the Impact of Ambient Stratification on Bottom Gravity Currents Tamay M. Özgökmen CPT Workshop II November 2004, RI

  2. Progress Report: • Özgökmen, Fischer, Duan and Iliescu, 2004: Three-dimensional turbulent bottom density currents from a high-order spectral element model. J. Phys. Oceanogr., 34/9, 2206-2026. • Özgökmen, Fischer, Duan, and Iliescu, 2004: Entrainment in bottom gravity currents over complex topography from three-dimensional nonhydrostatic simulations. Geophys. Res. Lett., 31, L13212. • Chang, Xu, Özgökmen, Chassignet, Peters, and Fischer: Comparison of gravity current mixing parameterizations and calibration using a high-resolution 3D nonhydrostatic spectral element model. Ocean Modelling, accepted.

  3. On-going Investigations: • Further testing with TP and KPP using HYCOM: Yeon Chang (& Özgökmen, Peters, Chassignet) • Time-dependent forcing: Silvie Matt (Özgökmen, Johns) • Development of SGS models for LES: Iliescu, Özgökmen, Fischer, Duan • Impact of ambient stratification: Özgökmen (& Johns, Fischer, Iliescu, Duan)

  4. Method: 3D Nonhydrostatic Spectral Element Model Nek5000developed by Paul Fischer Primary attributes of the spectral element method are: • Combines geometrical flexibility of finite element method and numerical accuracy of spectral expansion • Virtually free of spurious modes: minimal numerical dissipation and excellent phase properties • Dual approach to convergence: algebraic via elemental grid refinement and exponential via increase in spectral expansion order • Scalability on massively parallel machines: 1999 Gordon Bell Prize for nek5000 for a 3D fluid problem on 8168-processor ASCI-Red.

  5. Sample simulation with homogeneous ambient(bumpy topography)

  6. Motivation and Experimental Setup: • All simulations with homogeneous ambient so far: - no equilibrium can be reached - unrealistic for oceanic applications • What are the properties of “product” water masses? • Simulations with 3 slope angles, 6 different ambient stratifications: θ = 3°, 5°, 7° Rρ = αΔT/βΔS = 0, 1 .25, 1.7, 2.0, 2.5, 3.0 or: Tb = 2π/N (min) = inf, 25, 22, 20, 18, 16 REDSOX-1, northern channel lift-off: 19 < Tb < 47 (min) Rρ= 0 : unstratified reference exps Rρ= 1.25 : mild – no lift off within the domain All others : lift off

  7. Impact of ambient stratificationSpectral Element Model Simulation – 2Dsalinity: temperature:

  8. 3D Nonhydrostatic Spectral Element Simulation with ambient stratification

  9. First impressions:

  10. Separation Level:

  11. Propagation Speed:

  12. Product Salinity:

  13. Mass Transport:

  14. Main Results:

  15. 2D vs 3D:

  16. Plans Over the Next Year: • Further testing of TP and KPP based schemes using HYCOM using nonhydrostatic model results • HYCOM for the Red Sea Overflow

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